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J. Bacteriol., 12 1997, 7530-7537, Vol 179, No. 23
A Puskas, EP Greenberg, S Kaplan and AL Schaefer
Rhodobacter sphaeroides is a free-living, photoheterotrophic bacterium
known for its genomic and metabolic complexity. We have discovered that
this purple photosynthetic organism possesses a quorum-sensing system.
Quorum sensing occurs in a number of eukaryotic host-associated gram-
negative bacteria. In these bacteria there are two genes required for
quorum sensing, the luxR and luxI homologs, and there is an acylhomoserine
lactone signal molecule synthesized by the product of the luxI homolog. In
R. sphaeroides, synthesis of a novel homoserine lactone signal,
7,8-cis-N-(tetradecenoyl)homoserine lactone, is directed by a luxI homolog
termed cerI. Two open reading frames immediately upstream of cerI are
proposed to be components of the quorum-sensing system. The first of these
is a luxR homolog termed cerR, and the second is a small open reading frame
of 159 bp. Inactivation of cerI in R. sphaeroides results in mucoid colony
formation on agar and formation of large aggregates of cells in liquid
cultures. Clumping of CerI mutants in liquid culture is reversible upon
addition of the acylhomoserine lactone signal and represents a phenotype
unlike those controlled by quorum sensing in other bacteria.
Copyright © 1997, American Society for Microbiology
A quorum-sensing system in the free-living photosynthetic bacterium Rhodobacter sphaeroides
Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston 77224, USA.
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